Crack Detection in High Pressure Borehole Tubulars using Acoustic Emission

ABSTRACT

An acoustic emission sensor is placed on a tubular part and the part is subjected to rising pressure as readings are obtained. On some parts like swivel connectors, there must be a sensor on each moving component. The pressure is raised during testing to no more than 1.5 times the maximum allowable working pressure. Signals are detected by the sensors and results are displayed graphically and correlated on charts of Log duration v. amplitude and Log energy v. amplitude to reveal developing cracks. Extraneous noise such as rubbing, corrosion, or leaks will produce a different chart pattern and can be filtered out. Suspect components will be scrapped to avoid failure from further high pressure use.

CROSS REFERENCE TO RELATED APPLICATION

This application is claims priority from U.S. Provisional Patent Application Ser. No.: 62/277,695 filed on Jan. 12, 2016.

FIELD OF THE INVENTION

The field of the invention is a testing technique using acoustic emission to detect for cracks and wall thinning in high pressure flow iron and components having returned from pressure pumping operations or overpressure events to determine if damage from stress has occurred.

BACKGROUND OF THE INVENTION

Iron used in pressure pumping operations is inspected at periodic intervals for cracks on the exterior surface and at the threaded connections. The industry standard for detecting cracks is using magnetic particle inspection. It is a highly subjective test that sometimes produces inaccurate results based on the skill and training of the inspector. Other methods include a shear wave ultrasonic scan of the entire part or radiography. Both are expensive, time consuming, and require a highly trained technician not to mention the awareness of using nuclear sources.

A more objective test was needed to inspect high pressure oilfield iron that has returned from jobs under severe pressure and vibration conditions or if the iron has experienced pressures exceeding design limits. Micro cracks develop in locations with high stress risers and then propagate until fracture occurs, sometimes far below the design limits. Failure from iron fracture causes a loss of production which translates into expense for the operator and Service Company or at worst; causes injury or death. The acoustic emission test quickly inspects the entire component for cracks and removes the subjective interpretation of results.

Acoustic emission is a technique that has been used to detect cracks in drill bit cutting inserts in US 2013/0166214. The technique is also used to determine the effects of corrosion as shown in U.S. Pat. No. 7,246,516. Pressure vessels can be monitored using acoustic emission testing in the nuclear power generation industry as shown in U.S. Pat. No. 3,855,847. However, it only monitors the vessel under continuous operation and at pressures far below design levels. The present invention entails a quick pressure buildup above design limits to force open micro cracks for analysis. It is the only reliable method available to recertify a part that has been over-pressured and also has the ability to identify past occurrences of overpressure in the part.

Despite the long standing existence of acoustic emission technology, it has heretofore not been applied in this manner to the testing of high pressure tubular iron and components for micro cracks to determine if the part is fit for further service. Additionally, acoustic emission can do a full body scan for wall thinning from erosive and corrosive fluids during pumping operations. Current methods for detecting for minimum wall is to use hand held ultrasonic instruments to perform spot checks of local areas and not the entire pipe thereby allowing areas of wall thinning to go undetected.

The method of this patent uses acoustic emission technology to record and analyze shockwaves generated as micro cracks open under pressure during testing. The part is subjected to a rising step up in pressure, up to 150% of the maximum allowable working pressure. Data is gathered, evaluated, and displayed on charts that track Log duration v. amplitude and Log energy v. amplitude from the signals generated at one or more sensors attached to the iron. The shapes of the plots reveal the presence and severity of cracks, and the data can be further downloaded and passed through a program to give a reliable, objective, and consistent report on whether the part passes or fails. Additional analysis of the correlation plots will also detect for minimum wall thickness over the entire component. The complete process only takes a few minutes. These and other aspects of the present invention will be more readily apparent to those skilled in the art from a review of the detailed description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be determined by the appended claims.

SUMMARY OF THE INVENTION

An acoustic emission sensor is placed on a tubular part and the part is subjected to rising pressure as readings are obtained. On some parts like swivel connectors, there must be a sensor on each moving component. The pressure is raised during testing to no more than 1.5 times the maximum allowable working pressure. Signals are detected by the sensors and results are displayed graphically and correlated on charts of Log duration v. amplitude and Log energy v. amplitude to reveal developing cracks. Extraneous noise such as rubbing, corrosion, or leaks will produce a different chart pattern and can be filtered out. Suspect components will be scrapped to avoid failure from further high pressure use.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows sensor locations on a swivel;

FIG. 2 shows sensor locations on a straight joint;

FIG. 3 shows sensor location for an elbow;

FIG. 4 shows sensor location for a cross;

FIG. 5 is a logarithmic display of Log energy v. amplitude per hit of the signal from a test;

FIG. 6 is a logarithmic display of Log duration v. amplitude per hit of the signal from a test.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows locations for sensors 10, 12, 14, 16 and 18 on all the relatively rotating components of a multi-connection swivel. In FIG. 2, the sensors can be placed near either end or at opposed ends 20 and 22. FIG. 3 illustrates sensor 24 placement in the middle of an elbow. FIG. 4 locates sensor 26 in the middle of a cross. The sensor should be mounted using magnetic hold downs and adequate couplant applied to the sensor to enhance signal transmission. The center of the sensor face should be directly coupled to the surface of the iron. The surface in contact with the sensor face must be clean and free of particulate matter. Signal loss can be caused by certain types of paint or coatings, encapsulates, geometric discontinuities, and surface roughness. In certain cases, it may be necessary to reduce signal loss by locally removing corrosion, paint etc. from the surface of the metal.

After calibration, pressure is gradually increased and the resulting signals sensed and plotted in a variety of formats. The pressure is increased to about 1.5 times the maximum allowable working pressure for the component. The tail in FIG. 5 indicates the development of a major crack. The pattern of FIG. 6 near the top similarly indicates a tail as an indication of a major crack. The second and smaller tail below indicates minor cracks developing. Each individual hit signal (red dots on the graphs) is collected and analyzed in a separate program for pass/fail.

Those skilled in the art will appreciate that used parts recycled from other jobs may have been subjected to pressure or vibration that has initiated cracks and would not be detectable during an external visual inspection or within the part using a borescope. Running all these parts through x-ray would be cost prohibitive and require extensive safety measures. The method of the present invention allows mounting the acoustic emission sensor to the part and raising the pressure to a level not to exceed 1.5 times the maximum allowable working pressure to determine if cracks either exist or are developing in the part to a point where the part should be scrapped because it creates a significant risk for failure on its next use. The cracks can be either on the surface, hidden by corrosion, or below the surface. The methodology of generating and analyzing the signals is new in the sense that pressure is raised above the design limit in order to open any micro cracks that could lead to failure and to recertify iron that was over-pressured in the field. The testing can occur in the shop when the parts are returned after a job. Tubulars as well as connecting parts can be tested in minutes either individually or assembled as a string.

The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below. 

I claim:
 1. A used tubular or tubular connection testing method, comprising: mounting at least one acoustic emission sensor to the tubular or tubular connection; raising the internal pressure to as much as 1.5 times the maximum allowable working pressure for the tubular or tubular connection; tracking duration v. amplitude or energy v. amplitude signals from said at least one sensor; comparing information from said tracking to a standard to decide if the tubular or tubular connection is accepted for reuse or rejected.
 2. The method of claim 1, comprising; mounting a plurality of sensors when the tubular connection has relatively movable parts.
 3. The method of claim 1, comprising; graphing logarithmically duration v. amplitude or energy v. amplitude data from said at least one sensor.
 4. The method of claim 1, comprising; cleaning the surface of the tubular or tubular connection before attaching said at least one sensor.
 5. The method of claim 1, comprising; locating a center of a face of said at least one sensor directly to the tubular or tubular connection outer surface.
 6. The method of claim 3, comprising; determining if said graphing reveals one or more tails as an indication of cracking.
 7. The method of claim 1, comprising; using data from said at least one sensor to compute the minimum wall thickness of the tubular or tubular component.
 8. The method of claim 1, comprising; opening micro-cracks in the tubular or tubular component from said raising the internal pressure.
 9. The method of claim 1, comprising; mounting said at least one sensor with magnetic force.
 10. The method of claim 1, comprising; applying a couplant to said at least one sensor to enhance transmission.
 11. The method of claim 1, comprising; performing a full body wall thickness evaluation from data from said at least one sensor.
 12. The method of claim 1, comprising; performing said comparing for the tubular or tubular connection in a manner of minutes.
 13. The method of claim 1, comprising; performing said comparing in a shop after said tubular or tubular connection is returned from field service. 